Single element beam scanning apparatus having entrance and exit faces and a reflecting face therebetween

Abstract

To enable scanning by a light beam with a single unit of rotating optics, a light beam issuing from semiconductor laser 1 is launched into rotating lens mirror 3 through entrance face S 1 , thence directed to reflecting face S 2 , whereby it is deflected to leave the lens mirror 3 through exit face S 3 and form a spot that scans over the imaging plane.

We claim: 
     
       1. A beam scanning apparatus for scanning an object, comprising: a beam generator:   a single, rotatably supported, optical element having a reflecting surface, an entrance face and an exit face, at least one of said entrance face and said exit face having a predetermined shape for correcting aberrations in a light beam projected from said beam generator to said optical element, the light beam being introduced into said optical element through said entrance face, reflected by said reflecting face, and exiting through said exit face to the object to be scanned by said scanning apparatus; and   rotational drive means for driving said optical element in a scanning direction about an axis of rotation substantially orthogonal to a plane defined by the path of the light beam through said optical element.   
     
     
       2. A beam scanning apparatus according to claim 1 wherein said entrance face is concave and said exit face is convex. 
     
     
       3. A beam scanning apparatus according to claim 1 wherein said entrance face is convex and said exit face is concave. 
     
     
       4. A beam scanning apparatus according to claim 1 wherein at least one of said entrance face and said exit face are planar. 
     
     
       5. A beam scanning apparatus according to claim 1 wherein at least one of said entrance face and said exit face are aspheric. 
     
     
       6. A beam scanning apparatus according to claim 1 wherein at least one of said entrance face and said exit face are toric. 
     
     
       7. A beam scanning apparatus according to claim 1 wherein radii of curvature of said entrance and exit faces satisfy the following relationship:   (R.sub.1 -R.sub.2)/D+1/N.sup.2 =1     where N is the refractive index of said optical element, R 1  is the radius of curvature of said entrance face, R 2  is the radius of curvature of said exit face, and D is the distance between said entrance face and said exit face along an optical axis of the light beam in said optical element.   
     
     
       8. A beam scanning apparatus according to claim 1 wherein the rotating axis of said optical element is co-planar with said reflecting face. 
     
     
       9. A beam scanning apparatus according to claim 1 wherein the axis of rotation of said optical element lies inside the optical element when viewed in a sub-scanning direction. 
     
     
       10. A beam scanning apparatus according to claim 1 wherein the axis of rotation of said optical element lies outside the optical element when viewed in a sub-scanning direction, and on a side of said reflecting face opposite said entrance face and said exit face. 
     
     
       11. A beam scanning apparatus according to claim 1 wherein the optical axis of said entrance face is disposed at an angle with respect to the optical axis of said exit face when viewed in a cross section taken in a sub-scanning direction. 
     
     
       12. A beam scanning apparatus according to claim 1 wherein said optical element corrects only a curvature of field and astigmatism. 
     
     
       13. A beam scanning apparatus according to claim 1 further comprising imaging optics for focusing the light beam exiting through said exit face on an imaging plane of the object to be scanned. 
     
     
       14. A beam scanning apparatus according to claim 13 wherein said imaging optics comprises a reflecting mirror having a curved reflecting surface. 
     
     
       15. A beam scanning apparatus according to claim 13 wherein said imaging optics comprises a single lens. 
     
     
       16. A beam scanning apparatus according to claim 15 wherein said single lens has a positive refractive power. 
     
     
       17. A beam scanning apparatus for scanning an object, comprising: a beam generator;   a single, rotatably supported, optical element having a reflecting surface, an entrance face and an exit face, at least one of said entrance face and said exit face having a predetermined shape for correcting aberrations in a light beam projected from said beam generator to said optical element, the light beam being introduced into said optical element through said entrance face, reflected by said reflecting face, and exiting through said exit face to the object to be scanned by said scanning apparatus; and   rotational drive means for rotatably driving said optical element in a scanning direction, wherein the optical axis of said entrance face is disposed at an angle with respect to the optical axis of said exit face when viewed in a cross section taken in a sub-scanning direction of the optical element.